1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method, in which a substrate is coated with a chemical amplification type resist, followed by exposing the resist to light and subsequently processing the substrate before the developing processing.
2. Description of the Related Art
In a photolithography step, which is one of the steps of the semiconductor device manufacturing process, a semiconductor wafer is coated with a thin resist film, followed by exposing the resist film to light in a prescribed pattern and subsequently developing the patterned resist film so as to form a mask pattern. These processes are carried out in general by using a system including a resist coating-developing device, and a light exposure device connected to the resist coating-developing device.
On the other hand, a chemical amplification type resist material is being studied in recent years. In the chemical amplification type resist material, an acid is generated by the light exposure from an acid generating agent contained in the resist material, and the generated acid is diffused by the post-exposure bake so as to act as a catalyst. As a result, an acid catalytic reaction is allowed to proceed. For example, in a positive resist, a decomposition reaction for decomposing the base resin, which is a main component of the resist material, is generated in the portions of the resist corresponding to the light-exposed regions so as to make the portions soluble in a developing solution. On the other hand, in a negative resist, a crosslinking reaction is generated in the portions of the resist corresponding to the light-exposed regions so as to change the molecular structure of the base resin of the resist material, thereby making the portions insoluble in the developing solution. For example, the hydroxyl group of the polymer such as polyvinyl phenol is blocked by an alkyl group or a silyl group, and the block is removed by an acid so as to restore the solubility in an alkali.
FIGS. 1A to 1C show the states of a resist 102 in the light exposure step, the heating and the development step in the case of using a chemical amplification type negative resist. First, in the light exposure step, the resist 102 formed on a substrate 101 is exposed to light by using a mask 103 thereby generating protons (H+), which are an acid, on those surface portions of the resist 102 which were exposed to light. Then, the substrate 101 is heated from the back surface by using a heat source 104, thereby diffusing generated acid, i.e., the proton particles (H+), into the portions of the resist corresponding the light-exposed regions so as to make the light-exposed portions insoluble in the developing solution, as shown in FIG. 1B. After the heating step, the resist 102 is developed, thereby dissolving those portions of the resist 102 which are soluble in the developing solution to form a mask pattern as shown in FIG. 1C.
The use of the resist of this kind is advantageous in that it is possible in principle to comply with a fine line width. Since the developing rate of the chemical amplification type resist is determined by the amount of the acid catalytic reaction, the characteristics of the chemical amplification type resist, particularly, the accuracy in the line width of the mask pattern after the development, are greatly affected by the conditions of the heat treatment after the light exposure.
The heating device for heating the substrate after the light exposure step is constructed such that a substrate is disposed on a heating plate having a resistance heater buried therein, the substrate disposed on the heating plate is covered with a lid so as to form a processing space, and a purge gas stream flowing from, for example, the outward toward the central portion is formed within the processing space.
However, the heating device of the construction described above gives rise to the following problem. Specifically, the acid generated from the sensitizing agent by the exposure to light, i.e., proton (H+), is scattered from the surface portion of the resist 102 in the heating step so as to be diffused into the purge gas, as shown in FIG. 2A. As a result, that surface portion of the negative resist from which the acid of proton (H+) has been scattered remains to be soluble in the developing solution like the portions of the resist corresponding to the unexposed regions, though the particular surface portion, which has been exposed to light, should originally be rendered insoluble in the developing solution by the acid catalytic reaction. It follows that the upper portion of the mask pattern is rendered roundish so as to render poor the accuracy in the line width of the mask pattern as shown in FIG. 2B. On the other hand, in the positive resist, that surface portion from which the acid of proton (H+) has been scattered, remains to be insoluble in the developing solution like the portions of the resist corresponding to the unexposed regions, though the particular surface portion, which has been exposed to light, should originally be rendered soluble in the developing solution by the acid catalytic reaction. It follows that a lateral projection is formed in the upper portion of the mask pattern, i.e., a T-shaped top portion is formed, so as to render poor the accuracy in the line width of the mask pattern as shown in FIG. 2C. It should also be noted that, if the scattered proton (H+) is carried by the purge gas stream so as to be attached again to another portion of the resist, the portion that should originally be rendered soluble is rendered insoluble in the developing solution, or, by contraries, the portion that should originally be rendered insoluble is rendered soluble in the developing solution, so as to lower the accuracy of the pattern.
A TARC (Top Anti-Reflective Coating) treatment in which an antireflective film is coated is known as a means for preventing the acid of proton (H+) from being scattered from the surface portion of the resist film. In the TARC treatment, however, it is difficult to coat uniformly the antireflective film. Also, if the line width is rendered further narrower, it is difficult to obtain a high accuracy of the line width. In addition, the running cost is increased because the coating step is required.
On the other hand, in the post-exposure bake of a chemical amplification type resist, the initial distribution of protons (H+) in the portions of the resist corresponding to the light-exposed regions is not uniform. As a result, it is difficult for the chain reaction to take place uniformly so as to make it difficult to ensure a desired uniformity in the line width. Also, the required heating temperature is high, i.e., 100 to 150° C., in order to permit a sufficient reaction to take place in the portions of the low proton (H+) concentration in the portions of the resist corresponding to the light-exposed regions. The convection is increased with elevation of the temperature, with the result that a turbulence tends to be generated in the processing space so as to make the temperature nonuniform. It should also be noted that, since the initial distribution of the acid of protons (H) is not uniform as described above, it is necessary to set the light exposure amount at a high level so as to prevent the portion where proton (H+) is deficient from being formed, leading to the waste of energy. In addition, an inconvenience such as transpiration of the acid of proton (H+) is brought about as described above. Further, it is desirable to form an appropriate proton (H+) distribution conforming to the pattern in the portions of the resist corresponding to the light-exposed regions in order to improve the uniformity of the line width. In the conventional post-exposure bake treatment, however, it is difficult to form an appropriate proton (H+) distribution conforming to the pattern.